tests: Add unit tests for library functions

test/default.nix

@@ -13,9 +13,15 @@ let
   # The new Haskell infra applied to nix representation of Hackage
   haskell = import ../. hackage;
 
+  haskellLib = let hl = import ../lib { inherit lib; haskellLib = hl; }; in hl;
+
 in {
   cabal-simple = callPackage ./cabal-simple { inherit haskell; };
   cabal-22 = callPackage ./cabal-22 { inherit haskell; };
+
+  # Run unit tests with: nix-instantiate --eval --strict -A unit
+  # An empty list means success.
+  unit = callPackage ./unit.nix { inherit haskellLib; };
 }
 
 ## possible test cases

test/unit.nix

@@ -0,0 +1,54 @@
+{ lib, haskellLib }:
+
+let
+  emptyConfig = {
+    components = {
+       benchmarks = { };
+       exes = { };
+       foreignlibs = { };
+       library = "library";
+       sublibs = { };
+       tests = { };
+       all = "all";
+    };
+    package.identifier.name = "empty";
+  };
+
+  componentsConfig = {
+    components = {
+       benchmarks = { bbb = "bbb"; };
+       exes = { eee = "eee"; };
+       foreignlibs = { fff = "fff"; };
+       library = "library";
+       sublibs = { };
+       tests = { ttt = "ttt"; };
+       all = "all";
+    };
+    package.identifier.name = "nnn";
+  };
+
+in
+lib.runTests {
+  # identity function for applyComponents
+  test-applyComponents-id = {
+    expr = haskellLib.applyComponents (componentId: component: component) emptyConfig;
+    expected = emptyConfig.components;
+  };
+
+  # map a component to its component name and check these are correct
+  test-applyComponents-library = {
+    expr = haskellLib.applyComponents (componentId: component: componentId.cname) emptyConfig;
+    expected = emptyConfig.components // { library = "empty"; all = "empty"; };
+  };
+
+  test-applyComponents-components = {
+    expr = haskellLib.applyComponents (componentId: component: component) componentsConfig;
+    expected = componentsConfig.components;
+  };
+
+  # testing that the tests work
+  testId = {
+    expr = lib.id 1;
+    expected = 1;
+  };
+}